Carrier HH12ZB240 Limit Switch

The Carrier HH12ZB240 is a high-limit OEM replacement part engineered for precise thermal regulation and safety in Carrier, Bryant, and Payne gas furnaces. As a normally closed (NC) switch, it is designed to protect the heat exchanger from damage caused by restricted airflow or blower failure. This auto limit switch functions on a specific thermal cycle, opening the circuit when internal temperatures reach 240°F to interrupt the gas valve and closing once the plenum drops to 200°F.

For service technicians, the HH12ZB240 limit switch features a 3-inch extension probe to ensure accurate sensing within the supply air stream. It serves as a direct substitute for legacy ICP part numbers including HH12ZA240, HH12ZA252, and P331-2217. Maintaining these exact temperature specifications is critical for preventing system short-cycling and ensuring the furnace operates within its designed static pressure and heat-rise parameters. This component is essential for resolving common "overlimit" fault codes on the control board.

• Ensures furnace safety by preventing heat exchanger overheating and potential cracked cells.
• Features a 240F fixed setpoint to match original equipment manufacturer thermal protection curves.
• The automatic reset design eliminates manual intervention after the unit cools to 200°F.
• Includes a 3-inch insertion length for optimal thermal response in various plenum configurations.
• Compatible with a wide range of 340MAV, 350MAV, and 355MAV Carrier furnace models.

How do I test if the Carrier HH12ZB240 is faulty?
With the power off, use a multimeter to check for continuity across the terminals. Since this is a normally closed component, you should read zero ohms at room temperature. If the switch remains open (infinite resistance) while cool, it has failed and requires replacement.

What causes a limit switch to trip frequently?
Frequent tripping is usually a symptom of airflow restriction. Check for a dirty air filter, blocked return grilles, or a failing blower motor capacitor. If the furnace short cycles, the switch is performing its safety function to prevent damage to the heat exchanger.

Can I use a higher temperature limit switch as a substitute?
No. Using a switch with a higher opening point than the specified 240 degrees can lead to dangerous operating temperatures, potentially compromising the integrity of the heat exchanger or causing a fire hazard.

Disclaimer: While we strive for 100% accuracy, product data and specifications are subject to change. Please contact our team to confirm compatibility or technical details before purchasing.